Can anyone tell me what upgraded gearbox would work (or I could get to work) on this four wheeler. Has #3 gearbox and with 18V upgrade is way too slow. I have new 550 motors that will accept any pinion gears. I cant use the new motors with the #3 gearbox because I have tried a couple of 8 tooth 32 pitch pinion gears and they do not mesh correct - I assume the gearbox is not 32 pitch but have no idea what pitch it is. Also if I were able to upgrade to a 7 box would I need new tires because the existing hub in the tires is designed for the old pentagon hub. Any help would be appreciated. Thanks.